In the current specifications of the third generation mobile networks (referred to as UMTS), the system utilizes the same well-known architecture that has been used by all main second-generation systems. A block diagram of the system architecture of current UMTS network is presented in FIG. 1. The UMTS network architecture includes the core network (CN), the UMTS terrestrial radio access network (UTRAN), and the user equipment (UE). The core network is further connected to the external networks, i.e. Internet, PLMN, PSTN and/or ISDN.
The GSM Phase 1/2 Core Network consists of network switching subsystem (NSS). The NSS further consists of the following functional units: Mobile Switching Center (MSC), Visitor Location Register (VLR), Home Location Register (HLR), Authentication Center (AC) and equipment identity register (EIR). The GSM Phase 2+ enhancements to the GSM phase 1/2 CN are serving GPRS (General Packet Radio Service) support node (SGSN), gateway GPRS support node (GGSN) and CAMEL service environment. The most important new feature that is introduced with the GPRS is the packet switching (PS), which improves the capacity of the network.
The UTRAN architecture consists of several radio network subsystems (RNS). The RNS is further divided into the Radio Network Controller (RNC) and several base stations (BTS, referred to as B nodes in the 3rd Generation Partnership Project (3GPP) specifications).
In this architecture there are several different connections between the network elements. The Iu interface connects the CN to the UTRAN. The Iur interface enables the exchange of signaling information, as well as the establishment of user plane connections, between two RNCs. The signaling protocol across the Iur interface is called the Radio Network Subsystem Application Part (RNSAP). The RNSAP is terminated at both ends of the Iur interface by an RNC. The Iub interface connects an RNC and a node B. The Iub interface allows the RNC and node B to negotiate about radio resources, for example, to add and delete cells controlled by node B to support communication of dedicated connection between UE and S-RNC, information used to control the broadcast and paging channels, and information to be transported on the broadcast and paging channels. One node B can serve one or multiple cells. The UE is connected to node B through the Uu radio interface. The UE further consists of a subscriber identity module (USIM) and mobile equipment (ME). They are connected by the Cu interface. Connections to external networks are made through a gateway MSC (towards circuit switched networks) or GGSN (towards packet switched networks).
In order to obtain the most efficient RAN architecture, which is based on using the good characteristics of IP, some functionality has to be relocated between network elements. In the most revolutionary architecture we no longer have a network element commonly known as a BSC (Base Station Controller) or RNC (Radio Network Controller), although this functionality must remain in the RAN. In one embodiment of the IP RAN, there has been chosen to locate some RNC functionality in the BTSs to enable e.g. soft handover and associated signaling to happen along the shortest path, producing minimum delay and signaling load to those parts of networks where this is not necessary. Referring to the above state of art description it can be said that IP RAN is realized by implementing most of the RNC (or BSC) functionality in the BTS (IP BTS). Only Paging, basic O&M (Operation and Maintenance) and configurations, location calculation functions and common radio resource management may be implemented in separate servers outside the BTS site.
In the distributed architecture of IP RAN, the distributed functionalities of RNC/BSC from the CN's or neighboring radio network's point of view are hidden. In an IP RAN architecture, the introduction of the Radio Network Access Server (RNAS, a signaling GW) and Radio Access Network Gateway (RNGW)/Circuit Switched Gateway (CSGW) (user plane GWs) creates two instances of the Iu interface from the core network towards the IP BTS. The same happens with the Iur interface from a conventional RNC to an IP BTS. The presence of two instances of the Iu and Iur interfaces for interworking reasons is one of the main characteristic of the IP RAN Distributed architecture.
The IP RAN is a distributed architecture, where the RNAS and GWs are hiding the mobility to the core network. The current RAN architecture is not a distributed architecture. For a correct interworking of the two instances of Iu and Iur interfaces, the e.g. RNSAP and RANAP protocols in the inner instance of the interface (Iu′, Iur″) are not directly applicable. One problem is that the current RNC ID address space (12 bits) is not enough to specify the source IP BTS and target IP BTS in Iu′ interface during the relocation procedure. Additional problem is the addressing of connectionless messages in case of Iur″ interface (for example, Uplink Signaling Transfer, Paging Request). In this case, as far as the RNAS acts as interworking signaling unit, the identity of the receiving entity (RNC) has to be included into those messages so that RNAS can address properly this receiving entity.
Therefore, the RNSAP and RANAP protocols in the inner instance of the interface (Iu′, Iur″) need to be modified in the handling of the instance identifiers. Without the solution described in the present invention it is not possible to implement the IP radio access network.